SOHC.co.uk Forums > CB500/550

CB550 - full trottle performance

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Erny:
Thanks. Rising needles means carbs to pull and sync them again
Main jets change I can do with carbs on bike

But still wondering if this is not caused by something else as I have stock setup, I would expect default settings shall be fine (needle position, jets..)

K2-K6:
"Thanks. Rising needles means carbs to pull and sync them again
Main jets change I can do with carbs on bike"
it's certainly a pain if you have to change them. Suggested two steps as if you made one step and found improvement but not quite enough, then you'd have to do it all over again. Whereas jumping two steps answers the question of if it needs larger jets, if it's not successful then the next step is to consider a jet change.

They do different things,  needle height versus main jet size. The larger jet is focused on fuel demand at full revs and full throttle, the needle position changes the points at which the jetting changes in volume on the way there.

Needle position and idle air screw are never absolute fixed position.  They are there to compensate, in fine adjustment, for the jet sizes which are fixed. They need to be set for the environment and conditions in which you are running the engine and can quite happily be different from the manual which is always given as baseline setting from which to optimise.

deltarider:
All the aftermarket exhausts systems back in the day, advertised with: 'no rejetting required'. All, but one, which was a special Sebring 4-1 racing exhaust. I don't see why your bike, having such close to the original exhausts, would need bigger main jets. Air intake is stock, isn't it? Generally speaking I advise to leave the jet needles alone. My experience is limited to OEM parts however. Before you do anything, I'd have a look at the plug noses. If you have a dealer nearby, you may consider a run on a Dyno. Expect to need a 6% CO for a good driveability for a bike of that era.

K2-K6:
"Before you do anything, I'd have a look at the plug noses."

You'd have to run it consistently in the "error"range for the plug colour to mean anything reliable for that error,  which I doubt you could do.

Laverda Dave:
I would be tempted to go on a dyno. Might cost a bit more but at least you will have a full read out of what the engine is doing across the entire rev range and this will give you a chance to make small adjustments whilst you are there to potentially fix the problem.

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